Hitherto, SUS 316, which is generally said to exhibit the lowest ion elution among metal materials, has been used as material used in fuel cells or conventional secondary cell systems in order to keep the cooling efficiency thereof or prevent pipes from being blocked or corroded. However, the use of resin has been desired from the viewpoint of molding workability or a height of the flexibility of shapeability. The use of resin material such as polypropylene or polyvinylidene fluoride has been investigated.
For example, in the case of fuel cells for automobiles, the desire has been met by using material exhibiting a very low ion elution (such as SUS 316) as material of heat exchangers or pipes for circulating cooling liquid. In such a case, however, the shape of the heat exchangers or the fabricating method thereof is restricted. Thus, an increase in the size of the thermal exchangers, an increase in the weight thereof, an increase in costs, and others are caused. When metal material is used, metal ions may elute out gradually from the material itself or corrosion may advance from slight scratches in the surface thereof. There is a method for coping therewith by subjecting the inside of a heat exchanger to coating so as to decrease ion elution. However, if the coating deteriorates, ions may elute out (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2001-035519, and JP-A No. 2003-123804).
Accordingly, it has been desired to develop resin material as a substitute therefor. However, when the resin material is used in the form of a simple substance, products therefrom warp or deform. Dependently on the use environment thereof, the resin material is insufficient in heat resistance and rigidity. In order to compensate for these, an attempt of incorporating a filler such as talc, mica, glass fiber or calcium carbonate has been made.
Incidentally, these fillers are each inorganic powder obtained by pulverizing a mineral, and thus metal ions elute easily therefrom. In the case of, for example, talc, main components thereof are silicon dioxide and magnesium oxide. Besides, aluminum oxide, iron oxide, calcium oxide and so on are contained therein. As eluting cations, silicon, magnesium, aluminum, iron, calcium and other ions are detected. Besides, sodium, potassium and zinc ions are detected as impurity cations, and chloride ions, hydroxide ions and other ions are detected as anions. Accordingly, about composite compositions into which a filler is incorporated, metal ions elute out very much. Thus, the stability of physical properties thereof over a long term is also poor. As a result, there is a problem that the composition cannot be used.
Accordingly, an object of the invention is to provide a resin composition for a fuel cell member which gives only a small amount of eluting ions.